1. Field of the Invention
The present invention relates to pumps that suck and discharge fluid such as oil.
2. Description of the Related Art
As described in Japanese Patent Application Publication No. 2011-190763 (JP 2011-190763 A), an internal gear pump has an inner rotor having external teeth formed on its outer periphery, an outer rotor having internal teeth formed on its inner periphery, a housing having a pump chamber that accommodates the inner rotor and the outer rotor, and a plate attached to the housing in close contact therewith so as to close the pump chamber.
In the pump having such a structure, salt water such as seawater enters between the housing and the plate from the outside due to capillary action, and salt remains therebetween, which may cause rusting between the housing and the plate. This rust moves the housing and the plate away from each other, slightly separating the housing and the plate from each other. Side clearance between the inner rotor and the housing or plate or between the outer rotor and the housing or plate thus increases, which reduces capacity efficiency as the ratio of an actual discharge rate to a theoretical discharge rate.